During the production of polymers (e.g., polyolefins), feed components including one or more monomer (e.g., one or more olefin monomers such as ethylene), catalyst, diluent, and other possible polymerization components (e.g., hydrogen) are typically introduced into a polymerization reactor and mixed at desired conditions of temperature, pressure, and concentration to produce a polymer (e.g., a polyolefin, for example, polyethylene) having desired properties such as a certain density and molecular weight. The various components can be separately introduced directly to the polymerization reactor; alternatively, two or more of the feed components can be combined prior to introduction to the polymerization reactor.
A challenge in the production of polyolefins is to maintain production of polyolefin with desired properties during a production run. For example, the flow rate at which polymerization catalyst components are added to a polymerization reactor can affect the physical and mechanical properties of the polyolefin produced within the polymerization reactor. Dilute phase slurry feed is often utilized for catalyst and components in a slurry loop process. A variety of catalysts may be used, such as, without limitation, chromium-based catalysts, Ziegler-Natta catalysts, metallocene catalysts, non-metallocene catalysts, phosphate alumina catalysts, nickel catalysts, and the like. Generally, the different catalyst systems require different components, and dilutions/concentrations. The catalysts are typically diluted in one or more tanks and then fed to a polymerization reactor in a known concentration. These tanks can be expensive to both install and maintain.
Polyolefin plants (e.g., polyethylene plants) often employ multiple catalysts, which increase the tank requirement. Conventional technology generally utilizes charge tanks, mix tanks, and run tanks with diaphragm slurry pumps to pump the dilute mixtures into the polymerization reactor(s) or precontactor(s). Such equipment is often massive, complex, and difficult to clean out when changing from one catalyst type or system to another. Catalyst components can be added to a polymerization reactor in a variety of ways. For example, catalyst components may be introduced into a polymerization reactor(s) using ball check feeders, optionally in combination with mud pots. Ball check feeders typically include a rotating cylinder having a cavity on one side of the cylinder which fills with and empties catalyst components into the polymerization reactor after each 180° rotation of the cylinder. However, the amount of the catalyst components that fill the cavity during each rotation of the cylinder can vary, resulting in differing amounts of the catalyst components being fed to the polymerization reactor. Variations in concentration of catalyst result in variations in reaction rate. That is, different feed amounts of the catalyst components to the polymerization reactor can cause variances in operation and control of the polymerization reaction process occurring within the polymerization reactor, thus leading to variable production rates and the production of polyolefin with variable, undesired or less than ideal properties.
Some catalyst systems are operable via pre-contacting of the catalyst components or adjuvants, for example in a precontactor, prior to introduction into a polymerization reactor. For example, catalyst systems can comprise at least one catalyst, an activator, a support, a co-catalyst, or a combination thereof. The contact time of the catalyst components, and the consistency of contact time (e.g., the residence time in a precontactor) obtained by all of the catalyst particles, can affect process operability, catalyst performance, and product qualities.
An ongoing need thus exists for improved catalyst preparation and feeding techniques and systems therefor. Desirably, such preparation and feeding techniques and systems eliminate or reduce the conventionally-utilized mixing and dilution of catalyst upstream of a polymerization reactor or precontactor, thus eliminating or reducing the need for the charge tanks, mix tanks, and run tanks conventionally utilized; provide for more consistent contacting of catalyst components in a precontactor upstream of a polymerization reactor; or both.